One of the most popular post-emergent non-selective herbicides used around the world is glyphosate and salts of glyphosate including the monoammonium, diammonium and isopropyl ammonium salts disclosed in U.S. Pat. Nos. 5,998,332; 5,994,269; 5,196,044; 4,507,250; 4,481,026; 4,405,531; 4,315,765; 4,140,513; 3,977,860; 3,799,580; 3,799,758; and 3,853,530. Of these, the most widely sold non-selective herbicide in the world is the isopropylamine salt of N-(phosphonomethyl)glycine also named isopropylammonium glyphosate (“IPA glyphosate”).
Like many post-emergent herbicides, glyphosates and salts of glyphosates are generally slow-acting, even with the addition of surfactants. Such slow responses of the targeted weeds to the herbicidal composition fail to provide the desired phytotoxicity of the formulation for days, sometimes even weeks. This is undesirable from the user's standpoint, especially for home and garden users where the herbicide is used for aesthetic purposes by the purchaser.
Over the years, developments have focused on alternative formulations capable of improving the rapidity of plant response to glyphosate salt formulations. U.S. Pat. Nos. 5,196,044 and 6,503,869, for instance, disclose enhanced herbicidal compositions wherein an enhancer, such as pelargonic acid or salts of pelargonic acid, is added to the glyphosate salt in order to decrease the time for plant response Such developments have resulted in the commercial availability of IPA glyphosate herbicidal formulations to home owners in so-called “ready-to-use” (RTU) forms that, when sprayed on the targeted weed, causes the weed to wilt, turn color and die in short time periods, sometimes as short as 24 hours or less. Such RTU formulations containing IPA glyphosate employ between from about 0.75 to about 2% by weight of IPA glyphosate with similar amounts of enhancing agents. The balance of the formulation is inactive ingredients, such as surfactants and water.
For economic reasons, it is advantageous to package and sell post-emergent herbicides in concentrated forms, i.e., formulations having low or no solvent content. Such concentrated formulations save both sellers and buyers the cost of storing and shipping water in which the herbicide ingredients are soluble. Furthermore such concentrates allow the end-user to vary his desired herbicidal treatment by diluting the concentrate with water to the strength needed, e.g., a high water dilution for easily killed weeds and a lower dilution for larger weeds or brush.
Previously, glyphosate concentrates containing as much as 53 weight percent glyphosate have been introduced to buyers-users in place of RTU formulations. However, such concentrates are still slow acting when diluted for use unless they are combined with a bipyridilium salt such as Diquat®, an EPA restricted material undesirable for use.
Some of the most effective enhancement agents, while compatible with IPA glyphosate at dilute concentrations, are not capable of being dissolved in concentrated IPA glyphosate solutions and therefore do not offer a practical solution to manufacturers for concentrated forms of glyphosate salts. For example, commercially available unenhanced IPA glyphosate formulations typically contain from about 53.8 weight percent to as high as 62 weight percent IPA glyphosate in water. Attempts to incorporate enhancing agents, such as pelargonic acid or salts of pelargonic acid, into concentrated formulations have been unsuccessful in rendering homogeneous mixtures or solutions. This is attributable to chemical incompatibility. For example, when 18% or stronger IPA glyphosate in water is added to 40% or lower ammonium pelargonate in water, two liquid phases result, neither phase being soluble in the other. Such mixtures, having separate liquid phases, have no commercial value.